Mesoporous SiO₂ Particles Combined with Fe Oxide Nanoparticles as a Regenerative Methylene Blue Adsorbent

Mesoporous SiO₂ adsorbents were combined with Fe oxide nanoparticles (∼10 nm) that can catalyze thermal oxidation of organic compounds at low temperatures. Fe oxide nanoparticle (∼10 nm)-incorporated SiO₂ adsorbents were prepared via a temperature-regulated chemical vapor deposition method followed by a thermal annealing process. The removal efficiency and reusability of Fe oxide/SiO₂ particles were examined and compared to those of bare SiO₂. Upon deposition of Fe oxide nanoparticles, not only the equilibrium adsorption capacity of mesoporous SiO₂ for methylene blue (MB) was improved but also the reusability of SiO₂ adsorbent was increased significantly. The adsorption ability of fresh Fe oxide/SiO₂ particles can be almost fully recovered by simple thermal annealing at atmospheric conditions (400 °C), whereas that of bare SiO₂ reduced significantly under same conditions. In addition, full recovery of initial MB adsorption ability of Fe oxide/SiO₂ can be achieved by a 100 °C annealing process. Fourier transform infrared, thermogravimetric analysis, and X-ray photoelectron spectroscopy analyses indicated that Fe oxide nanoparticles catalyzed thermal degradation of adsorbed MB molecules, resulting in the improved reusability of the Fe oxide/SiO₂ adsorbent. In addition to reusability, the equilibrium adsorption capacity of mesoporous SiO₂ particles for various cationic dye molecules, such as MB, malachite green, and rhodamine B, can be improved by combining Fe oxide nanoparticles.